In many parts of the world due to inadequate rainfall it is necessary at certain times during the year to artificially water turf and landscaping. An ideal irrigation system for turf and landscaping should utilize a minimum number of valves, supply lines and sprinklers. Preferably the valves should be turned ON and OFF by an inexpensive, yet reliable electronic irrigation controller that is easy to program and can carry out a wide variety of watering schedules. The goal is to uniformly distribute the optimum amount of water over a given area. The type, placement and flow rates for each of the sprinklers are pre-selected when an irrigation system is designed and/or installed.
Residential and commercial irrigation systems typically include one or more solenoid actuated valves that are turned ON and OFF by the electronic irrigation controller. The valves admit water to various subterranean branch lines usually made of PVC pipe that typically have several sprinklers connected to risers coupled to the branch lines at spaced intervals. Each combination of a solenoid valve and its associated sprinklers is referred to in the irrigation industry as a station or zone. A modern electronic irrigation controller typically includes a microprocessor that executes one or more watering programs. Typically the watering programs can be pre-programmed by the user via push button and/or rotary controls. The watering programs contain one or more watering schedules which consist of run and cycle times for each station. The controller usually has an LCD or other display to facilitate programming by the user. Often the controller will revert to a default watering program in the case of a power failure. The microprocessor actuates the solenoid valves via suitable drivers and switching devices. The valves are opened and closed by the microprocessor in accordance with the pre-programmed run and cycle times for each of the stations.
Homeowners, conservationists and water purveyors are increasingly interested in minimizing the amount of water used for irrigation, especially in areas like the Southwest where water is in short supply. Some municipalities have enacted restrictions on residential and commercial watering. While such restrictions do save water, they are often arbitrary and do not take into account the watering needs of different types of vegetation in different geographic locations. Techniques have been developed for tailoring watering schedules in an electronic irrigation controller to accommodate different kinds ofplants and atmospheric conditions based on evapotranspiration (ET) rate. This is a number that represents the amount of water lost by a plant via evaporation in the surrounding soil, as well as the amount of water lost by the plant through transpiration, i.e. loss of water through its leaves or foliage. See for example U.S. Pat. No. 5,097,861 granted Mar. 24, 1992 to Hopkins et al. and assigned to Hunter Industries, Inc. of San Marcos, Calif., which discloses a controller that utilizes stored historic ET data for each zip code, along with other stored data, to calculate watering schedules.
Irrigation controllers that have the internal capability of calculating their watering schedules based on ET rates are typically complicated to use and expensive to buy. Separate after-market ET units which “piggy back” onto a base controller with no internal ET capability have limited utility because they can only reduce the existing watering schedules in the base controller.